Summary Transposons are used as robust, precise genetic tools in a range of model and nonmodelorganisms in which, through techniques such as gene tagging and trapping andenhancer trapping, they have enabled the identification of genes based on their function.This technology has complimented whole genome projects and accelerated genediscovery. In many organisms, transposons have a clear applied function in enablinggenetic transformation to occur and high frequency transformation is now standard in them. In medicine, transposons are now sought as human gene therapy vectors. In mosquitoes however, complete transposon-based genetic technology is yet to be fully established. Transposons from three separate families are used to generate transformants at low frequencies, however none can be remobilized at any reasonablefrequency in the germ-line and the widely used piggyBac transposon becomes dormant even in the soma. As a result the gene discovery technologies that abound in otherorganisms still lag far behind in mosquitoes, despite the availability of whole genomeprojects for these pests. This proposal seeks to develop transposons as truly robust genetic tools in Aedes aegypti through the understanding and circumvention of recentlydiscovered small RNA pathways (piRNA) that in other animals, regulate transpositionin both the germ-line and the soma. We present data demonstrating the presence ofthese pathways in wild-type and transgenic lines of Ae. aegypti. We describe experiments that will enable the comprehensive characterization of these pathways in Ae. aegypti. We will experimentally address their ability to silence newly introducedtransposons with respect to the timing of this immune response and to whetherendogenous mosquito transposon small RNAs with sequence homologies to these newtransposons can also trigger this response. We outline three strategies that we believe can circumvent the piRNA response of Ae. aegypti. The ability to use transposons aseffective genetic tools in mosquitoes will accelerate the pace of gene discovery and sodirectly increase the ability to identify and use mosquito genes in a wide range ofgenetic and chemical control strategies designed to reduce the spread of pathogens by these insect vectors.